In general, power transmitting apparatuses for motorcycles are intended to arbitrarily transmit or cut off driving force of an engine to a transmission and a driving wheel. Such power transmitting apparatuses typically includes an input member, output member and clutch member. The input member is connected to the engine side. The output member is connected to the transmission and the driving wheel side. The clutch member is connected to the output member. The power is transmitted by bringing a plurality of driving clutch plates and driven clutch plates into pressure contact. The transmission of the power is cut off by releasing the pressure-contact force.
More specifically, a conventional power transmitting apparatus includes, as disclosed, for example in JP2013-137039, a clutch housing. The clutch housing rotates with the rotation of an input member. A plurality of driving clutch plates is formed on the clutch housing. A plurality of driven clutch plates are alternately formed with the driving clutch plates of the clutch housing. A clutch member is connected to an output member. A pressure member, attached to the clutch member, is movable in the axial direction of the clutch member. The pressure member brings the driving clutch plates and the driven clutch plates into pressure contact or release pressure-contact by its axial movement relative to the clutch member. The pressure member is configured to transmit or cut off rotational force input to the input member to the output member by bringing the driving clutch plates and the driven clutch plates into pressure contact or releasing pressure-contact force.
The above conventional power transmitting apparatus further has a pressure-contact assist cam and a back torque limitation cam. When the rotational force input to the input member is transmitted to the output member and the pressure member and the clutch member rotate relative to each other, the pressure assist cam can move the pressure member and the clutch member closer to each other. This increases the pressure-contact force between the driving clutch plates and the driven clutch plates. When the rotation of the output member exceeds the rotational speed of the input member and the pressure member and the clutch member rotate relative to each other, a back pressure limiter cam moves the pressure member and the clutch member away from each other. This releases the pressure-contact force between the driving clutch plates and the driven clutch plates. The pressure-contact assist cam and back torque limiter cam are each formed by opposing cam surfaces formed on the pressure member and the clutch member. When the pressure member and the clutch member rotate relative to each other to the normal rotation side, the pressure-contact assist cam operates. When the pressure member and the clutch member rotate relative to each other to the reverse rotation side, the back torque limiter cam operates. The torque, when the back torque limiter cam operates, and the torque, when the pressure-contact assisting cam operates, is preferably variously set according to needs, such as the form of a vehicle and driver's preferences.